Safety for fastener driving tool

ABSTRACT

A fastener driving or applying tool includes a fluid actuated cycle valve for controlling a main valve to move through an automatic sequence of opening and closing movements to operate a piston actuated fastener driving blade through power and return strokes. In two embodiments, the degree of bias applied to the cycle valve is varied to provide a single cycle of power and return strokes (single cycle tool) or a series of such cycles (multifire tool). The tool includes a trigger or firing control and a safety control, and a fluid actuated piston prevents movement of the cycle valve unless the safety control is actuated prior to the firing control.

United States Patent Ramspeck et al.

[ June 10, 1975 SAFETY FOR FASTENER DRIVING TOOL PrimaryExaminer-Granville Y. Custer, Jr. [75] lnvemors' 23:31: :kgz jfzgzgngfig Anomey, Agent, or Firm-Mason, Kolehmainen,

both of m Rathburn & Wyss [73] Assignee: Duo-Fast Corporation, Franklin[57] ABSTRACT Park' A fastener driving or applying tool includes a fluidac- [22] Filed: Sept. 13, 1973 tuated cycle valve for controlling a mainvalve to move through an automatic sequence of opening and [21] Appl'397,021 closing movements to operate a piston actuated fastener drivingblade through power and return strokes. 52 US. Cl 227/8; 227/130 In twoembodiments. the degree of bias pp to the s [1 Int. Cl. B250 1/04 cyclevalve is varied to Provide a Single cycle of Power [581 Field at Search227/7, 8, 130; 91/356 and return Strokes g cycle 1001) or a series ofsuch cycles (multifire tool). The tool includes a trigger [56]References Cited or firing control and a safety control, and a fluidactu- UNITED STATES PATENTS ated piston prevents movement of the cyclevalve un- I less the safety control is actuated prior to the firing3,278JO3 l/l966 .lullfs et al 227/l30 control 3.638.532 2/l972 227/l30 X3,685,396 8/ I972 Obergfcll 227/130 X 14 Claims, 9 Drawing Figures l ll1 62 l;

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fiA"? 3O I Q F6--% E l 46 l "l 4? 64* i 65-? SAFETY FOR FASTENER DRIVINGTOOL This invention relates to a fastener applying tool and. moreparticularly, to such a tool with automatic stroke sequences and a newand improved safety therefor.

A safety standard that is becoming increasingly applicable to poweractuated fastener driving tools including pneumatic nailers and staplersis one requiring the tool to be disposed against the workpiece beforethe operation ofa firing control, such as a trigger. US. Pat. Nos.3,677,456 and 3,677,457 disclose two arrangements for inhibitingoperation of fastener driving tools when a trigger control is operatedprior to a safety control. The arrangements shown in these two patentsare ones in which a main valve assembly controlling the supply ofpressurized fluid to and the exhaust of fluid from the drive cylinder isopened and closed directly by the trigger control and the safetycontrol. However, there are a number of nailers and staplers using cyclevalves to provide automatic opening and closing sequences of the mainvalve, and it would be desirable to provide a safety-bcfore-triggersafety control for this type of tool.

Accordingly. one object of the present invention is to provide a new andimproved control for a fastener applying tool.

Another object is to provide a fastener applying tool of the typeincluding a cycle valve which includes means for preventing operation ofthe tool unless a workpiece engaging safety is actuated prior to afiring control.

A further object is to provide a new and improved safety for automaticmain valve sequence fastener driving tools, which safety includes afluid actuated piston for inhibiting initiation of a sequence ofoperations of the main valve.

A further object is to provide a safety for a fastener driving toolusing a cycle valve in which a movable fluid actuated pistonmechanically blocks movement of the cycle valve when a safety controland a firing control are operated in an improper sequence.

In accordance with these and many other objects, an embodiment of thepresent invention comprises a fastener driving tool including a maincylinder containing a drive piston for actuating a fastener drivingblade. A main valve is operable to opened and closed positions to supplypressurized fluid to and exhaust fluid from the main cylinder,respectively. The movement of the main valve to its opened and closedpositions to provide power and return strokes of the fastener drivingblade is controlled by a fluid actuated cycle valve having twomagnitudes of fluid bias applied thereto so as to obtain either singlecycle or multifire operation. A pneumatic piston disposed in a positionin which it can be moved into an abutting mechanical relationship withthe cycle valve is selectively controlled by a workpiece engaging safetyand a firing or trigger control to mechanically block movement of thecycle valve whenever the firing control is actuated prior to the safety.In the multifire embodiment, the locking piston also includes valvemeans for selectively applying the bias necessary for multifireoperation only after it has been determined that the safety control hasbeen actuated prior to the trigger or firing control.

Many other objects and advantages of the present invention will becomeapparent from considering the following detailed description inconjunction with the drawings in which:

FIG. I is an elevational view in partial section illustrating thefastener driving tool embodying the present invention;

FIG. 2 is a schematic diagram of the pneumatic control circuit used inthe tool shown in FIG. I to provide single cycle operation;

FIG. 3 is a schematic diagram illustrating the fluid controls used inthe tool shown in FIG. I to obtain multifire operation;

FIG. 4 is an enlarged sectional view taken along line 4-4 in FIG. 1illustrating a multiflre control valve assembly shown in normalposition;

FIG. 5 is a sectional view taken along line 5-5 in FIG. 4 illustrating acombined safety and trigger or firing control;

FIG. 6 is a sectional view taken along line 6-6 in FIG. 4 illustrating acycle valve and sequence control piston included in the control valveassembly;

FIG. 7 is a fragmentary sectional view similar to FIG. 4 illustratingthe control valve assembly after the operation of the safety control andprior to the operation of the firing control during a proper sequence ofoperation;

FIG. 8 is a fragmentary sectional view similar to FIG. 4 illustratingthe control valve assembly on an improper operating sequence in whichthe firing control has been actuated prior to the safety control; and

FIG. 9 is a fragmentary sectional view similar to FIG. 6 illustrating aportion of a cycle valve for attaining sin gle cycle operation in themanner shown achematically in FIG. 2 of the drawings.

Referring now more specifically to FIG. I of the drawings, therein isillustrated a fastener driving tool which is indicated generally as 20and which embodies the present invention. The fastener driving tool 20includes a housing 22 having a forward or head portion 22A defining achamber 24 continuously supplied with pressurized fluid such ascompressed air from a reservoir defined by a hollow rearwardly extendinghandle portion 228 of the housing 22. A drive cylinder 26 disposed inthe chamber 24 slidably receives a drive piston 28 to which the upperend of a fastener driving blade or element 30 is connected. The lowerend of the driver blade 30 is slidably received within a drive track 32formed in a nosepiece structure 34 forming a part of the housing 22. Aconventional magazine assembly indicated generally as 36 suppliessuccessive staples 38 from a strip thereof to the drive track 32 belowthe lower end of the driver blade 30.

A main valve assembly 40 in a normal closed condition connects the upperend of the interior of the cylinder 26 to the atmosphere and can bemoved to an open position to supply pressurized fluid to the cylinder 26to move the piston 28 and connected driver blade 30 through a powerstroke. The main valve assembly 40 is automatically moved through thiscycle of operation by a cycle valve in a control valve assemblyindicated generally as 42. The control valve assembly 42 is controlledby a conventional workpiece engaging mechanism indicated generally as 44and a firing control or manual trigger 46. The control valve assembly 42is arranged so that the main valve 40 cannot be moved to an openposition if the trigger 46 is actuated prior to operation of the safetymechanism 44 by placing the nosepiece structure 34 against a workpiece.

The construction of the tool 20 can be of any of the types well known inthe art and can, for example. be

constructed as shown and described in detail in US. Pat. No. 3.638.532.In general. the combined main and exhaust valve assembly 40 is normallyheld in a closed position by a plurality of compression springs 50 andpressurized air admitted to an annular chamber 52 over a passageway 54by the control valve assembly 42, the chamber 52 being formed in aclosure cap 56 for the tool 20. With the main valve assembly 40 in itsnormal position. communication between the pressurized fluid in thechamber 24 and the upper interior of the cylinder 26 is closed off. andthis upper interior is connected to the atmosphere over a system ofpassageways including a plurality of passageways 58 formed in theclosure cap 56. When the control valve assembly 42 is actuated by themanual trigger 46 and the workpiece engaging assembly 44, the chamber 52is vented to the atmosphere over the passageway 54 by the control valveassembly 42. and the main valve assembly 40 moves upwardly to close theconnection to atmosphere above the upper interior of chamber 26 and toplace the upper interior of the cylinder 26 in communication with thepressurized fluid in the chamber 24. This drives the piston 28downwardly through a power stroke during which the lower end of thefastener driving blade 30 engages a staple 38 disposed in the drivetrack 32 and drives this staple into a workpiece.

When the piston 28 reaches the lower end of its power or drive strokedetermined by engagement with a resilient bumper 60, pressurized fluidfrom the interior of the cylinder 26 flows through one or more openings62 in the piston 28 and through one or more ports 64 to be collectedwithin a fluid return chamber 66. This pressurized fluid is alsosupplied as a control signal to the control valve assembly 42.

When the control valve assembly 42 initiates a return stroke of thepiston 28, pressurized fluid is again supplied over the passageway 54 tothe chamber 52. This pneumatic bias coupled with the bias provided bythe springs 50 moves the main valve 40 downwardly so that it again seatson the upper end of the cylinder 26 to close off communication with thepressurized fluid in the chamber 24. In this position the main valveassembly 40 also opens the exhaust passages 58 so that the interior ofthe cylinder 26 above the piston 28 is con nected to the atmosphere. Atthis time pressurized fluid enters the interior of the cylinder 26 belowthe piston 28 through one or a number of ports 68. This compressed airforces the piston 28 upwardly to the normal position shown in FIG. 1.The piston is retained in this position by an O-ring 70 on the pistonwhich rests on a shoulder formed in the upper end of the cylinder 26.The air below the piston 28 leaks to the atmosphere around the lower endof the driver blade 30 and through the drive track 32 so that at theconclusion of the return stroke of the piston. both the lower end of theinterior of the cylinder 26 and the air return chamber 66 are placedsubstantially at atmospheric pressure.

The workpiece engaging assembly or means 44 which is actuated when thetool 20 is placed adjacent a workpiece can be of any suitable well knownconstruction. such as that shown in US. Pat. No. 365,049, In general,the assembly 44 includes a linkage or mechanism 72 mounted on thehousing 22 and the nosepiece struc ture 34 and resiliently biased to aposition in which a workpiece engaging portion 72A of the mechanismprojects downwardly below the lower end of the nosepiece structure 34.An upper portion 728 of the mechanism 72 is coupled by a lost motionarrangement to the lower end of a safety valve stem 74 forming apart ofthe control valve assembly 42. The illustrated lost motion couplingincludes a pair of spaced enlargements or collars 748 on the valve stem74. When the tool 20 is placed adjacent the workpiece, the lower endportion 72A engages the workpiece and moves the mechanism 72 upwardly.The upper portion 728, after taking up the lost motion between thespaced collars 74B, engages the upper collar 748 to move the valve stem74 upwardly. When the tool 20 is moved away from the workpiece, theresilient biasing means 75 moves the linkage 72 downwardly so that afterlost motion is taken up. the portion 72B engages the lower collar 748 tomove the valve stem 74 to the normal position shown in FIG. 1.

Referring now more specifically to FIG. 3 of the drawings. therein isillustrated in schematic form the control valve assembly 42 foroperating the tool 20 as an autofire tool in which the piston 28 willrepeatedly cycle through power and return strokes within the cylinder 26so long as the work engaging assembly 44 and the trigger 46 remainoperated. The control valve assembly 42 is such that the workpieceengaging assem bly 44 must be actuated to shift the safety valve stem 74before the trigger 46 is operated in order to enable the control valveassembly 42 to produce operation of the tool 20. As illustrated in theschematic diagram, in the normal condition of the tool 20, the mainvalve assembly 40 connects the upper interior of the cylinder 26 to theatmosphere. In this normal condition, a continuous pneumatic biasapplied to a piston portion 40A tending to open the main valve 40 isovercome by the pneumatic bias applied to a greater area piston portion408 by a cycle valve 76. In the physical embodiment of FIG. 1, thepiston portion 40B includes the larger, upper area of the annular valvedisposed in the chamber 52, and the piston portion 40A includes thesmaller. lower area exposed to the fluid pressure in the chamber 24.

In the normal condition of the tool 20, a valve 78 controlled by thesafety stem 74 normally supplies pressurized fluid to a piston 80 whichis mechanically coupled to the cycle valve 76 as indicated in dashedline to hold the cycle valve 76 in the illustrated position in whichpressurized fluid is supplied to the piston portion 408 of the mainvalve assembly 40. The bias applied by the piston 80 overcomes the biasapplied in an opposite direction by a piston portion 76A on the cyclevalve which is normally connected to pressurized fluid through a valveassembly 82 controlled jointly by the trigger 46 and the workpieceengaging assembly 44. A second piston portion 768 on the cycle valve 76providing a biasing force similarly directed to the piston portion 76Ais used to effect autofire operation. A greater area piston portion 76Cis provided for biasing the cycle valve 76 in an opposite direction. Thepiston portion 768 is normally connected to the atmosphere through theports 64 at the lower end of the cylinder 26 through a valve 84controlled by the piston 80. A passage to the piston portion 76C isnormally blocked at a valve 86 controlled by the piston 80.

Assuming that the tool 20 is to be placed in operation to provideautoflre operation in the correct sequence, the workpiece engagingassembly 44 is first actuated to move the valve stem 74 upwardly so thatthe valve 78 first shifts to its alternate position. In this position.the

piston 80 is connected to the atmosphere. and the bias applied to thepiston portion 76A through the valve 82 is effective to shift the cyclevalve 76 to its alternate position. This movement of the cycle valve 76mechanically moves the piston 80 to its released position in which thestate of the valves 84 and 86 controlled thereby are shifted. When thevalve 84 is shifted, pressurized fluid applied to the autofire pistonportion 768 to provide the bias necessary to effect cyclic autofireoperation of the cycle valve 76. The operation of the valve 86 connectsthe piston portion 76C to the port 64 to receive fluid pressure when thepiston 28 reaches the end of its power stroke. The bias applied to thepiston portions 76A and 76B holds the cycle valve 76 in its alternateposition so that the piston portion 403 on the main valve assembly 40 isconnected through the cycle valve 76 to the valve 82 controlled by thesafety stem 74 and the trigger 46.

When the trigger 46 is operated after the actuation of the workpieceengaging assembly 44 in the desired sequence, the valve 82 is shifted toits alternate setting and the piston portion 40B on the main valveassembly 40 is connected to the atmosphere. This permits the continuousbias applied to the piston portion 40A of the main valve 40 to open themain valve assembly and supply compressed air to the upper interior ofthe cylinder 26 while closing off the connection to the atmosphere. Thismoves the piston 28 downwardly through a power stroke during which astable 38 is driven into a workpiece.

When the piston 28 reaches the bottom of its power stroke, pressurizedfluid supplied by the main valve assembly 40 enters the port 64 in thelower end of the drive cylinder 26 (FIGS. 1 and 3) and is supplied tothe piston portion 76C. The greater area piston portion 76C provides abiasing force greater than that supplied by the piston portion 76B, theportion 76A now being connected to the atmosphere through the operatedvalve 82. Thus, the piston portion 76C shifts the cycle valve 76 to thesetting shown in FIG. 3 in which pressurized fluid is again applied tothe piston portion 408. This closes the main valve by shifting the mainvalve assembly 40 to the position illustrated in FIG. 3. In thisposition, the upper interior of the cylinder 26 is connected to theatmosphere, and the piston 28 is moved through a return stroke in themanner described above.

When the piston 28 has been returned to its normal position, thepressurized air in the lower end of the cylinder 26 leaks to theatmosphere in the manner described above, and thus pressurized fluidfrom the piston portion 76C on the cycle valve 76 leaks to theatmosphere through the port 64. When this pressure is decreasedsufficiently, the bias applied to the piston portion 76B shifts thecycle valve 76 to its alternate position so that the piston portion 408is again connected to the atmosphere through the cycle valve 76 and theoperated valve 82. This opens the main valve 40 by shifting the valveassembly 40 to its alternate position, and another power stroke of thepiston 28 is initiated. This operation continues until such time as thetrigger 46 and the workpiece engaging assembly 44 are released. Whenthese elements are released, the valves 78 and 82 return to the positionshown in FIG. 3. When the valve 78 is released, the pneumatic bias isagain applied to the piston 80, and this piston forces the cycle valve76 to its illustrated state in which pressurized fluid is again appliedto the piston portion 403 to hold the main valve assembly 40 in itsclosed state. In addition, when the piston is shifted, the valve 84 ismoved to its illustrated position in which the piston portion 768 isconnected to the atmosphere through the port 64. This removes theautofire bias from the piston portion 768 of the cycle valve 76. Whenthe valve 82 is released, bias is reapplied to the piston portion 76A ofthe cycle valve, and pressurized fluid is applied to the connection ofthe valve 82 to the cycle valve 76 so that the piston portion 40B cannotbe connected to the atmosphere until such time as the valve 82 isoperated.

The control valve assembly 42 is such that the autofire operation of thetool 20 described above cannot be initiated whenever the trigger 46 isactuated to shift the valve 82 to its alternate state prior to theoperation of the valve 78 to its alternate state by actuation of theworkpiece engaging assembly 44. More specifically, when the valve 82 isactuated first to its alternate state, this valve connects the pistonportion 76A to the atmosphere so that the only bias applied to the cyclevalve 76 tending to shift it to its alternate state is removed.Accordingly, when and if the workpiece engaging assembly 74 isthereafter operated to shift the valve 78 to its alternate state, thepiston portion 80 is again con nected to the atmosphere. However, sincethis piston portion is moved as described above through mechanicalengagement with the cycle valve 76 and since no bias is now applied byeither of the piston portions 76A or 768 to the cycle valve, the cyclevalve 76 remains in the setting illustrated in FIG. 3, and pressurizedfluid remains applied to the piston portion 408 of the main valveassembly 40 so that this valve cannot be moved to its open condition.Accordingly, the valve 82 must be released to its setting shown in FIG.3 to reapply a bias to the piston portion 76A followed by operation ofthe valve 78 by the workpiece engaging assembly 44 before autofireoperation of the tool 20 can be initi ated.

The mechanical construction and implementation of the valving shown inFIG. 3 is illustrated in FIGS. 4-8 of the drawings. The mechanicalconstruction of the control valve assembly 42 can be of any suitabletype and can, for example, be of the general nature disclosed anddescribed in US. Pat. No. 3,685,396. In general, the control valveassembly 42 is carried in a valve housing 88 as an integral subassemblywhich can be secured to a wall of the head portion 22A of the housing 22by suitable fasteners such as machine bolts or screws 90. Passages inthe valve housing 88 communicating with the various control componentsare coupled to ports terminating related passageways formed in thehousing 22. A mechanical arrangement other than those described belowcan be devised for carrying out the control functions described abovewith reference to FIG. 3 of the drawings.

FIGS. 4-6 of the drawings illustrate the control valve assembly 42 inits normal position. The housing 88 includes a bore 92 (FIGS. 4 and 5)open at its opposite end to the atmosphere and in which is slidablymounted the safety valve stem 74. The normal position of the valve stem74 is set by engagement of a locating washer 94 by a shoulder formed onthe valve stem 74. The valve stem 74 in cooperation with the bore 92defines the valve 78 and also carries and forms a part of the valve 82.

To pro. ide the valve 78, the valve stem 74 carries a pair of spacedO-rings 96 and 98 between which termi nates a passageway 100communicating with pressurized fluid in the chamber 24 so that the areabetween the O-rings 96 and 98 within the bore 92 is continuouslysupplied with pressurized fluid. This fluid normally passes through apassageway 102 (FIG. 4) to the lower end of a second valve bore 104 inthe housing 88 in which is slidably mounted the bias piston 80. Thepressurized fluid supplied over the passageway 102 normally biases thepiston 80 to the position shown in FIG. 4 in which it is set byengagement of the piston with a sleeve 106 disposed within the bore 104.In this position, a projection 80A engages the lower end of an elongatedpiston member 108 forming a part of the cycle valve 76 to hold the cyclevalve 76 in the normal position illustrated in FIG. 3 of the drawings.

When the valve stem 74 is moved upwardly to effect the functionalactuation of the valve 78 shown in FIG. 3, the valve stem 74 is moved tothe position shown in FIG. 7 in which the lower O-ring 96 is disposedabove the point in the bore 92 at which the passageway terminates. Thisconnects the passageway 102 and thus the lower end of the bore 104beneath the piston 80 to the atmosphere through the bore 92 inasmuch asthe interface between the washer 94 and the cylindrical portion of thevalve stem 74 is not sealed. In this manner, the valve 78 shown in FIG.3 is provided by the passageway 100, the O-ring 96, and the portterminating the passageway 102 within the bore 92.

To provide the valve 82 (FIG. 3) operated by conjoint actuation of theworkpiece engaging assembly 44 and the trigger 46, there is provided arecess 110 in the upper end of the valve stem 74 in which is movablymounted a valve member 112. The chamber or recess 110 is supplied withpressurized fluid at its lower end from the passageway 100 by an opening114 (FIG. 4) passing through the valve stem 74 to the chamber or recess110. Pressurized fluid supplied to the chamber 110 biases the valveelement 112 upwardly so that an enlargement 112A thereon seats on anO-ring 116 carried on the valve stem 74, thereby sealing offcommunication between the chamber 110 and the atmosphere. In the normalcondition of the valve 82, the pressurized fluid within the chamber 110passes through an opening 118 in the valve stem 74 and a portion of thebore 92 sealed by a further O-ring 120 carried on the valve stem 74 anda passageway 122 to be supplied to the cycle valve 76 through an openingin a sleeve 124 dis posed in the upper end of the bore 104.

To operate the valve 82 to its alternate setting from that illustratedschematically in FIG. 3, both the trigger 46 and the workpiece engagingassembly 44 must be operated. When the workpiece engaging assembly 44 isoperated. the valve stem 74 is moved upwardly to the position shown inFIG. 7. If the trigger 46 is then pivoted in a counterclockwisedirection (FIG. the trigger 46 engages the outer end of the valveelement 112 and moves it downwardly so that the enlarged portion 112Amoves out of engagement with the O-ring 116. This connects the chamber110 to the atmosphere through the open upper end of the bore 92. Thismovement of the valve element 112 also moves an O-ring 126 carried onits lower end into engagement with a tapered or sloping wall surface onthe valve stem 74 providing a valve seat and closes off communicationbetween the passageway 114 and the passageway 118.

This terminates the supply of pressurized fluid from the passageway tothe passageway 122. Thus, the cycle valve 76 is connected to theatmosphere over the passageway 122 and the operated valve 82.

The cycle valve 76 (FIGS. 4 and 6) includes the piston member 108 andadjacent portions of the sleeves 106 and 124 and the bore 104. Theportion of the bore 104 intermediate the sleeves I06 and 124 isconnected over the passageway 54m the chamber 52 (FIG. 1) in which isdisposed the large surface piston portion 408 (FIG. 3) of the main valveassembly 40. In the normal position of the piston member 108 to which itis biased by the piston 80, an O-ring 128 on the piston member 108 isout of engagement with the upper end of the sleeve 106 so that thepassageway 54 is in communication with pressurized fluid supplied by thechamber 24 through a passageway 130. The passageway 54 is held out ofcommunication with the passageway 122 to which pressurized fluid issupplied by the valve 82 in its normal condition by an O-ring 132 whichis carried on the piston 108 and which is seated on the lower end of thesleeve 124. When the cycle valve 76 is moved to the alternate positionshown in FIG. 7, the O-ring 128 seats on the upper end of the sleeve 106to close off communication between the passageways S4 and 130., and theO-ring 132 moves out of engagement at the lower end of the sleeve 124 toconnect the passageway 54 to the passageway 122 controlled by the valve82.

To relate various portions of the piston 108 to the piston portions 76A,76B. and 76C of the cycle valve 76 referred to in the description ofFIG. 3, the lower end of the piston 108 provides the piston portion 76Cand is so designated. The uppermost portion of the piston 108 which isdisposed within a reduced diameter portion 104A of the bore provides thepiston portion 76B. The next lowest portion of the piston 108 which isof a slightly larger diameter than the piston portion 76B provides thepiston portion 76A which is selectively supplied with a biasing pressureover the passageway 122.

The valves 84 and 86 (FIG. 3) that are selectively opened and closed bythe piston 80 are provided by three O-rings 134, 136, and 138 carried onthe piston 80 and movable within the lower end of the valve bore 104.The upper O-ring 134 normally closes off communication between thepiston portion 76C on the piston 108 (FIGS. 3 and 6) and a passageway(FIG. 6) extending from the bore 104 to the air return chamber 66. Thus,the passageway 140 normally does not provide communication between thepiston portion 76C and the port 64 in the cylinder 26. When the piston80 drops to its displaced position (FIG. 7 the passageway 140 is placedin communication with the piston portion 76C within the lower end of thesleeve 106. Thus, the O-ring 134 on the piston 80 provides the valve 86shown schematically in FIG. 3.

The O-rings 134 and 136 in the normal position of the piston 80 alsoplace the passageway 140 in communication with a passageway 142 (FIG. 6)extending at the upper end of the reduced diameter portion 104A of thevalve bore 104. Accordingly, the valve bore 104A is normally placed incommunication with the atmosphere over the passageways 140 and 142, theair return chamber 66, and the ports 64. The O-ring 136 normally closesoff communication between the passageway 142 and a passageway 144directly supplied with pressurized fluid from the chamber 24.

When the piston 80 is displaced to its lower position (FIG. 7), theO-ring I34 closes off communication between the passageways I40 and 142,and the Oring 136 places the passageway 142 in communication with thepassageway 144. Thus, pressurized fluid from the chamber 24 is nowsupplied to the piston portion 768 in the valve bore 104A to provide anautofire bias to the cycle valve 76. Thus, the O-rings 134 and 136 andthe cooperating structures including the passageways I30, 144, and 142provide the valve 84 shown schematically in FIG. 3.

When the tool is to be operated in its proper sequence, this tool isplaced against a workpiece so that the valve stem 74 is moved upwardlyfrom the normal position shown in FIG. 4 to the actuated position shownin FIG. 7. As the O-ring 96 passes the termination of the passageway102, compressed air normally holding the piston 80 in the position shownin FIG. 4 is vented to the atmosphere through the lower portion of thevalve bore 92. Since compressed air is continuously supplied from thepassageway 100 through the openings I14 and 118 and the passageway 122to the piston portion 76A on the piston 108, the piston 108 movesdownwardly from the position shown in FIG. 4 to the position shown inFIG. 7. In moving to this position, the O-ring 128 engages the adjacentportion of the sleeve 106 to close off communication between thepassageway 54 and the pressurized fluid inlet passage 130. Since theO-ring 132 has moved out of engagement with the adjacent end of thesleeve 124, the passageway 54 extending to the main valve assembly 40 isnow connected to the passageway 122 and receives pressurized fluidsupplied from the passageway 100.

Further, when the piston 80 moves downwardly from the position shown inFIG. 4 to the position shown in FIG. 7, the O-ring 134 places thepassageway 140 in communication with the open lower end of the sleeve106 so that pressurized fluid subsequently accumulated in the returnchamber 66 through the ports 64 can pass over the passageway 140 to thepiston portion 76C. The O-ring 134 also closes off communication betweenthe passageways 140 and 142 and places the passageway ]42 incommunication with pressurized fluid supplied from the passageway 144 sothat an autofire bias is forwarded over the passageway 142 to the pistonportion 768 on the piston 108.

Thus, following the actuation of the work engaging assembly 44 to shiftthe safety valve stem 74 to the position shown in FIG. 7, the componentsof the control valve assembly 42 are moved to the position shown in FIG.7.

With the components in this position, actuating the trigger 46 to theposition shown in dot and dash outline in FIG. 5 moves the triggerportion 46 shown in FIG. 7 downwardly against the upper end of the valveelement 112 to move it down so that the O-ring 126 seats on the adjacentportion of the valve stem 74 to close off communication between thepassageway 122 and the passageway 100. This removes the source ofclosing fluid bias for the large piston portion 408 of the main valveassembly 40. This downward movement of the valve element 112 moves theenlarged portion 112A out of engagement with the O-ring 116 so that thepassageway 122 is connected to the atmosphere. This discharges thepressurized fluid from the large area piston portion 408 and permits themain valve 40 to be opened by the small area biasing portion 40Acontinuously supplied with fluid from the chamber 24. Accord ingly, themain valve 40 is opened to initiate a power stroke of the piston 28 inthe driver blade 30 in the manner described above. At the end of thispower stroke, pressurized fluid from the interior of the cylinder 26passes through the ports 64 to be accumulated within the chamber 66 andthen passes over the passageway 140.

This fluid accumulates in the area in the bore 104 above the O-ring 134on the piston and acts on the piston portion 76C of the piston 108.Since the effective area of the piston portion 76C is greater than theeffective area of the piston portion 768, the pressure supplied throughthe passageway I40 moves the piston I08 upwardly to the normal positionshown in FIG. 4. In doing so, the O-ring 132 seats on the sleeve 124 andthe O-ring 128 moves out of engagement with the sleeve 106. Thisconnects the passageway 54 to the pressurized fluid supplied through thepassageway 130, and the pressurized fluid thus supplied to thepassageway 54 acts on the large area piston portion 408 of the mainvalve assembly 40 to move this valve assembly to its closed condition.This initiates a return stroke of the piston 28 in the manner describedabove.

Incident to this return stroke, pressurized fluid collected in thereturn chamber 66 is dissipated to the atmosphere through the ports 64and 68, and the bias applied to the piston portion 76B on the piston 108exceeds the bias applied to the piston portion 76C thereon. This movesthe piston 108 back to the position shown in FIG. 7, and pressurizedfluid is exhausted from the chamber 52 (FIG. 1) in the main valveassembly 40 so that the main valve assembly 40 again opens to initiate asecond cycle of operation of the tool 20. This cyclic operationcontinues under the control of the bias applied to the piston portions768 and 76C so long as the trigger 46 remains depressed or actuated, andthe workpiece engaging assembly 44 is operated.

Whenever these two assemblies or either one of these assemblies isreleased, the valve element 112 is moved upwardly by the pneumatic biassupplied through the passageway so that the enlarged portion 112A seatson the O-ring 116 and the ()-ring 126 moves out of engagement with theadjacent portion of the valve stem 74. This returns pressurized fluid tothe passageway 122 for holding the main valve 40 closed in the mannerdescribed above. Further, when the safety mechanism 44 is released, theO-ring 96 moves below the port terminating passageway 102 (FIG. 4). Atthis time, pressurized fluid from the passageway 100 flows over thepassageway 102 and into the lower end of the valve bore 104. This movesthe piston 80 upwardly to bias and hold the piston 108 in the normalposition shown in FIG. 4. In addition, the bias applied over thepassageway 142 (FIG. 6) to the autoflre piston portion 76B is dischargedto atmosphere over the passageway 140, and the supply of biasing fluidpreviously available from the passageway 144 is intercepted by theO-ring 136. In addition, the O-ring 134 cuts off the piston portion 76Con the piston 108 from communication with the signal passageway 140. Thetool 20 can be placed in multifire operation in the manner describedabove by first actuating the workpiece engaging assembly 44 followed bythe actuation of the manual trigger or firing control 46.

Assuming, however, that an attempt is made to operate the tool 20 in animproper sequence, the trigger 46 is first actuated fully to theposition shown in dot and dash outline in FIG. 5. This moves the trigger46 to the position shown in section in FIG. 8. If the tool is then movedtoward the workpiece, the safety valve stem 74 begins to move upwardly.However, when the valve stem 74 reaches the position shown in FIG. 8,the prior full actuation of the trigger 46 causes the valve element 112in the valve assembly 82 to move down wardly to the position shown inFIG. 8 at a time prior to movement of the O-ring 96 above the portterminat' ing the passageway [02. When the valve element 112 moves down,the O-ring 126 again interrupts the con nection between the passageway122 and the source of pressurized fluid provided by the passageway [00.This movement of the valve element 112 also moves the enlarged portion112A thereon out of engagement with the O-ring H6 so that the passageway[22 is connected to the atmosphere. This discharges pressurized fluidacting on the piston portion 76A of the piston 108 in the cycle valve 76and removes the only bias tending to move the piston 108 downwardly asviewed in FIG. 8.

Accordingly, if the tool 20 is thereafter placed against the workpieceso that the safety valve stem 74 becomes sufficiently elevated to movethe O-ring 96 above the port terminating the passage 102, pressurizedfluid acting on the lower surface of the piston 80 within the valvechamber 104 is again discharged to the atmosphere through the open lowerend of the valve bore 92. However, the piston 80 is held in the positionshown in FIG. 8 by the resilient O-rings 134, 136, and 138 inasmuch asthere are no pneumatic biases acting on either the piston 80 or thepiston 108 in the cycle valve assembly 76. Since the piston 108 remainsin the position shown in FIG. 8, the passageway 54 leading to the mainvalve assembly 40 remains connected to the pressurized fluid suppliedthrough the passageway 130 because the O-ring H8 is not seated on theupper end of the sleeve 106. The passageway 54 cannot be connected tothe atmosphere because the O-ring 132 remains seated on the sleeve 124.Thus, a cycle of operation of the tool cannot be initiated at this time.

If the manual trigger 46 is released so that the fluid pressure suppliedthrough the passageway 100 can again restore the valve 82 including thevalve element 112 to the normal position shown in FIGS. 4 and 7, thepassageway 122 is again pressurized, and the piston portion 76A canprovide a downwardly directed force shifting both the piston 80 and thepiston 108 to the lower position shown in FIG. 7. This permits theinitiation of multiflrc operation.

Accordingly, the control valve assembly 42 includes means for preventinginitiation of autofire operation of the tool 20 unless this tool isfirst placed against the workpiece to actuate the assembly 44 followedby manual actuation of the trigger 46. The piston 80 holds the piston108 in the cycle valve assembly 76 in its normal position when the valve82 controlled by the trigger 46 in the assembly 44 is operated prior tothe valve 78 controlled by the workpiece engaging assembly 44. When thetrigger 46 is first operated, the bias for moving the cycle valve 76normally applied to the piston portion 76A is removed which means thatthe control piston 80 remains in its elevated position and that thevalve means 84 and 86 (FIG. 3) remain in their normal settings so thatan autofire bias cannot be applied to the piston portion 768 and so thatthe passage 140 supplying a fluid pressure signal to the piston portion76C cannot be opened.

The control valve assembly 42 can also be provided in a modified form42A to provide single cycle operation rather than multifire operation.In single cycle operation, the drive piston 28 moves through one powerand return cycle and remains in this position even though the trigger 46and the workpiece engaging assembly 44 remain actuated until such timeas at least one of these components is released and reoperated. Thismodified control assembly 42A (FIG. 2) also insures that the tool 20cannot be operated through even the single cycle of operation unless theworkpiece engaging assembly 44 is actuated prior to the manual trigger46.

The only mechanical modification required in the control valve assembly42 to provide the single cycle control valve assembly 42A is illustratedin FIG. 9 of the drawings. More specifically, the passageway 142normally connecting the reduced diameter portion 104A of the valve borefor the cycle valve 76 is plugged or not provided. and the upper end ofthe reduced diameter portion 104A is vented to the atmosphere through apassageway 150. Thus, the piston portion 768 on the piston 108 for thecycle valve assembly 76 cannot be supplied with the pneumatic biasrequired for multifire operation. ln other respects, the single cyclecontrol valve assembly 42A is identical to the control valve assembly42.

A schematic diagram of the control valve assembly 42A for providingsingle cycle operation is illustrated in FIG. 2 of the drawings. in thisschematic diagram the valve 84 has been omitted as well as the pistonportion 768 inasmuch as these components perform no useful function. Thevalves and controlling mechanism shown schematically in FIG. 2 arerealized by the same mechanical structures described above with themodifications shown in FIG. 9.

Assuming that the tool 20 is to be operated in a proper sequence, thistool is placed against a workpiece, and the valve stem 74 moves upwardlyto first actuate the valve 78. When the valve 78 is actuated to itsalternate setting, compressed air is vented from the control piston 80.The bias supplied by the valve 82 for the piston portion 76A moves thecycle valve 76 to its alternate setting, and in doing so forces thepiston downwardly within the valve bore 104 to the position shown inFIG. 7. This actuates the valve 86 so that the piston portion 76C isplaced in communication with the ports 64 over the passageway and theair return chamber 66. When the cycle valve 76 moves to its alternatesetting, the piston portion 408 on the main valve assembly 40 is coupledto the valve 82.

When the valve 82 is next actuated by fully depressing the trigger 46,the piston portion 408 is connected to the atmosphere, and the pistonportion 40A is effective to shift the main valve assembly 40 to itsalternate setting so that compressed air is supplied to the upperinterior of the cylinder 26. This moves the piston 28 and the driverblade 30 through a power stroke during which a stable 38 is driven. Whenthe piston 28 reaches the end of its power stroke, pressurized fluidfrom the upper interior of the cylinder 26 is forwarded through theports 64 and the actuated valve 86 to the piston portion 76C. This biasimmediately shifts the cycle valve 76 to its normal position illustratedin FIG. 2 inasmuch as the prior actuation of the valve 82 removes allbias from the piston portion 76A. When the cycle valve 76 returns tothis setting, pressurized fluid is again applied to the piston portion408 of the main valve assembly 40, and this valve assembly moves to itsillustrated closed setting in which the upper interior of the cylinder26 is connected to the atmosphere. This permits the return of the piston28 to its normal position as described above.

The control valve assembly 42A remains in this position with the cyclevalve 76 in the position illustrated in FIG. 2 holding the main valveassembly 40 closed inasmuch as no bias is applied to the cycle valve 76to permit its return to an operated position when the air acting on thepiston portion 76C is dissipated to the atmosphere through the ports 64in the manner described above. The frictional engagement of the O-ringson the piston 108 (FIG. 3) in the cycle valve assembly 76 retains thepiston in the position shown in FIG. 4 in the absence of a bias. Whenthe trigger 46 is released and the workpiece engaging assembly 44 isreleased, the valves 78 and 82 return to the normal settings iilustratedin FIG. 2. This restores the piston 80 to a position biasing or blockingthe piston 108 of the cycle valve assembly 76 in its normal position.This movement of the piston 80 also opens the valve 86 so that thepiston portion 76C on the cycle valve 76 is no longer connected to theport 64. The reapplieation of bias from the valve 82 to the pistonportion 76A is not effective to shift the cycle valve 76 inasmuch as thebias provided thereby is less than the bias afforded by the controlpiston 80.

If an attempt is made to initiate a single cycle operation of the tool20 by first operating the trigger 46 followed by the operation of theworkpiece engaging assembly 44, the valve 82 is first operated to removethe bias from the piston portion 76A, and the valve 78 is thereafteroperated to remove the pneumatic bias from the control piston 80. As setforth above, the resilience of the O-rings on the pistons 80 and I08prevents movement of these pistons from the normal position shown inFIG. 4 because no pneumatic biases are effective on any of thesepistons. This means that the cycle valve 76 cannot be moved from itsnormal position shown schematically in FIG. 2 in which it supplies acontinuous connection of pressurized fluid to the large piston portion408 of the main valve assembly 40. This means that the main valveassembly 40 cannot be operated from its normal and illustrated closedstate in which the upper interior of the cylinder 26 is connected to theatmosphere. Accordingly, a single cycle operation of the tool 20 cannotbe initiated if the workpiece engaging assembly 44 is not actuated priorto the operation of the manual trigger 46. By releasing and reoperatingthe trigger 46, a single cycle operation of the tool 20 can beinitiated.

Although the present invention has been described with reference to anumber of illustrative embodiments thereof, it should be understood thatnumerous other modifications and embodiments can be devised by thoseskilled in the art that will fall within the spirit and scope of theprinciples of the present invention.

We claim:

1. A tool for driving fasteners into a workpiece comprising a poweredfastener driving assembly including a driver element actuated by a drivepiston movable within a cylinder,

a fluid controlled main valve means opened to supply pressurized fluidto and closed to exhaust fluid from the cylinder,

a fluid controlled cycle valve coupled to the main valve means andmovable to alternate positions to control opening and closing of themain valve means,

a first control means coupled to the cycle valve including a valvecontrolled by independently operable manual means and safety meansactuated by placing the tool adjacent the workpiece for moving the cyclevalve to a position effecting opening of the main valve means only whenboth of the manual means and the safety means are actuated.

and a second control means coupled to the cycle valve and responsive tothe operation of at least one of the manual means and safety means forpreventing movement of the cycle valve when the manual means is operatedprior to the safety means.

2. A tool for driving fasteners into a workpiece comprising a poweredfastener driving assembly including a driver element actuated by a drivepiston movable within a cylinder,

a fluid controlled main valve means opened to supply pressurized fluidto and closed to exhaust fluid from the cylinder,

a fluid controlled cycle valve coupled to the main valve means andmovable to alternate positions to control opening and closing of themain valve means, said cycle valve including at least one fluidresponsive surface for moving the cycle valve to one of said alternatepositions,

a first control means coupled to the cycle valve including independentlyoperable manual means and safety means actuated by placing the tooladjacent the workpiece for moving the cycle valve to a positioneffecting opening of the main valve means only when both of the manualmeans and the safety means are actuated,

and a second control means coupled to said fluid responsive surface onthe cycle valve for preventing movement of the cycle valve by preventingthe supply of fluid to the fluid responsive surface when the manualmeans is operated prior to the safety means.

3. A tool for driving fasteners into a workpiece comprising a poweredfastener driving assembly including a driver element actuated by a drivepiston movable within a cylinder,

a fluid controlled main valve means opened to supply pressurized fluidto and closed to exhaust fluid from the cylinder,

a fluid controlled cycle valve coupled to the main valve means andmovable to alternate positions to control opening and closing of themain valve means. said cycle valve being movable to a position effectingclosing of the main valve means under the control of fluid supplied tothe cylinder,

a first control means coupled to the cycle valve including independentlyoperable manual means and safety means actuated by placing the tooladjacent the workpiece for moving the cycle valve to a positioneffecting opening of the main valve means only when both of the manualmeans and the safety means are actuated.

and a second control means coupled to the cycle valve and to the firstcontrol means for preventing movement of the cycle valve after themanual means and the safety means are operated when the manual means isoperated prior to the safety means.

4. The tool set forth in claim 3 in which the second control meansincludes a fluid actuated piston mechanically coupled to the cycle valveand biasing the cycle valve against movement to a position effectingopening of the main valve means.

5. A tool for driving fasteners into a workpiece comprising a poweredfastener driving assembly including a driver element actuated by a drivepiston movable within a cylinder,

a fluid controlled main valve means for selectively supplyingpressurized fluid to and exhausting fluid from the cylinder,

a cycle valve coupled to the main valve means and movable to alternatepositions to control opening and closing of the main valve means,

a first control means coupled to the cycle valve including manual meansand safety means actuated by placing the tool adjacent the workpiece formoving the cycle valve to said main valve opening control position whenboth of the manual means and the safety means are actuated,

a second control means coupled to the cycle valve and to the cylinderfor moving the cycle valve to, said main valve closing control position,

a fluid actuated control piston coupled to the cycle valve forcontrolling its movement,

and means coupling the control piston to the first control means andcontrolling the control piston to prevent movement of the cycle valve tosaid opening control position when the manual means is actuated prior tothe safety means.

6. The tool set forth in claim 5 including means mounting the controlpiston for movement into and out of engagement with the cycle valve.

7. The tool set forth in claim 6 in which the first control meansincludes means for applying a biasing force to the control piston tohold the control piston in engagement with the cycle valve to preventmovement of the cycle valve when the manual means is actuated prior tothe safety means, said first control means rendering said biasing meansineffective when the safety means is actuated.

8. A tool for driving fasteners into a workpiece comprising a poweredfastener driving assembly including a driver clement actuated by a drivepiston movable within a cylinder through power and return strokes,

a fluid controlled main valve means that is opened to supply pressurizedfluid to and that is closed to exhaust fluid from the cylinder,

a cycle valve coupled to the main valve means and movable between afirst position to control opening of the main valve means and a secondposition to control closing of the main valve means,

a first control means coupled to the cycle valve in cluding manual meansand safety means actuated by placing the tool adjacent the workpiece formoving the cycle valve to its first position when both of the manualmeans and the safety means are actuated,

a second control means coupled to the cycle valve and to the cylinderfor moving the cycle valve to its second position when the piston hasmoved through its power stroke,

a fluid actuated control piston normally preventing movement of thecycle valve to its first position, means coupling the control piston tothe first control means,

and release means in the first control means for controlling movement ofthe control piston to permit movement of the cycle valve to said onefirst posi tion only when the safety means is actuated prior to themanual means.

9. The tool set forth in claim 8 in which the release means includesvalve means controlled by the safety means for selectively supplying anexhaust connection and pressurized fluid to the fluid actuated controlpistonv 10. A tool for driving fasteners into a workpiece comprising apowered fastener driving assembly including a driver element actuated bya drive piston movable within a cylinder,

a fluid controlled main valve means for selectively supplyingpressurized fluid to and exhausting fluid from the cylinder,

a cycle valve coupled to the main valve means and cyclically movable toalternate positions to control opening and closing of the main valvemeans,

a first control means coupled to the cycle valve including independentlyoperable manual means and safety means actuated by placing the tooladjacent the workpiece for initiating cyclic movement of the cycle valvebetween its alternate positions when both of the manual means and thesafety means are actuated,

and a second control means coupled to the cycle valve and the firstcontrol means for preventing cyclic movement of the cycle valve afterthe safety means and manual means are operated whenever the manual meansis operated prior to the safety means.

11. The tool set forth in claim 10 in which the second control meansincludes a fluid actuated bias valve for applying a fluid bias to thecycle valve,

and the first control means includes valve means for selectivelyconnecting the bias valve to pressurized fluid and an exhaust.

12. A multiflre tool for driving a series of fasteners into a workpiececomprising a powered fastener driving assembly including a driverelement actuated by a drive piston movable within a cylinder,

a fluid controlled main valve means for selectively supplyingpressurized fluid to and exhausting fluid from the cylinder,

at fluid operated cycle valve coupled to the main valve means andmovable to alternate positions to control opening and closing of themain valve means,

bias valve means for applying a fluid bias to the cycle valve means tomove the cycle valve means to one of its alternate positions,

means coupled to the cycle valve and to the cylinder for applying afluid bias to the cycle valve means to move the cycle valve to the otherof its alternate positions,

and control means including manual means and safety means actuated byplacing the tool adjacent the workpiece for initiating movement of thecycle valve when both of the manual means and the safety means areactuated. said control means including means operating the bias valvemeans to apply a fluid bias to the cycle valve means only when thesafety means is actuated prior to the manual means.

13. A tool for driving fasteners into a workpiece comprising a poweredfastener driving assembly including a driver element actuated by a drivepiston movable within a drive cylinder,

a fluid controlled main valve means for selectively supplyingpressurized fluid to and exhausting fluid from the cylinder,

a cycle valve coupled to the main valve means and movable to alternatepositions to control opening and closing of the main valve means, saidcycle valve including a valve cylinder and a valve piston movabletherein for controlling the connection of exhaust and pressurized fluidto the main valve means a piston means movable within the valve cylinderbetween a position biasing the valve piston and a position spaced fromthe valve piston.

first passage means placing the valve cylinder in communication with thedrive cylinder at a point located between the piston means and the valvepiston for applying a fluid bias from the drive cylinder to the valvepiston,

second passage means communicating with the valve cylinder at a pointspaced from the valve piston to apply a fluid bias to the piston meansonly,

and valve means controlling the application of fluid pressure to thesecond passage means.

14. A tool for driving fasteners into a workpiece comprising a poweredfastener driving assembly including a driver clement actuated by a drivepiston movable within a cylinder,

main assembly means opened to supply pressurized fluid to and closed toexhaust fluid from the cylindcr.

cycle means coupled to the main assembly means and movable to alternatepositions to control opening and closing of the main assembly means,

a first control means coupled to the cycle means including meanscontrolled by independently operable manual means and safety meansactuated by placing the tool adjacent the workpiece for moving the cyclemeans to a position effecting opening of the main assembly means onlywhen both of the manual means and the safety means are actuated,

and a second control means coupled to the cycle means and responsive tothe operation of at least one of the manual means and safety means forpreventing movement of the cycle means when the manual means is operatedprior to the safety

1. A tool for driving fasteners into a workpiece comprising a poweredfastener driving assembly including a driver element actuated by a drivepiston movable within a cylinder, a fluid controlled main valve meansopened to supply pressurized fluid to and closed to exhaust fluid fromthe cylinder, a fluid controlled cycle valve coupled to the main valvemeans and movable to alternate positions to control opening and closingof the main valve means, a first control means coupled to the cyclevalve including a valve controlled by independently operable manualmeans and safety means actuated by placing the tool adjacent theworkpiece for moving the cycle valve to a position effecting opening ofthe main valve means only when both of the manual means and the safetymeans are actuated, and a second control means coupled to the cyclevalve and responsive to the operation of at least one of the manualmeans and safety means for preventing movement of the cycle valve whenthe manual means is operated prior to the safety means.
 2. A tool fordriving fasteners into a workpiece comprising a powered fastener drivingassembly including a driver element actuated by a drive piston movablewithin a cylinder, a fluid controlled main valve means opened to supplypressurized fluid to and closed to exhaust fluid from the cylinder, afluid controlled cycle valve coupled to the main valve means and movableto alternate positions to control opening and closing of the main valvemeans, said cycle valve including at least one fluid responsive surfacefor moving the cycle valve to one of said alternate positions, a firstcontrol means coupled to the cycle valve including independentlyoperable manual means and safety means actuated by placing the tooladjacent the workpiece for moving the cycle valve to a positioneffecting opening of the main valve means only when both of the manualmeans and the safety means are actuated, and a second control meanscoupled to said fluid responsive surface on the cycle valve forpreventing movement of the cycle valve by preventing the supply of fluidto the fluid responsive surface when the manual means is operated priorto the safety means.
 3. A tool for driving fasteners into a workpiececomprising a powered fastener driving assembly including a driverelement actuated by a drive piston movable within a cylinder, a fluidcontrolled main valve means opened to supply pressurized fluid to andclosed to exhaust fluid from the cylinder, a fluid controlled cyclevalve coupled to the main valve means and movable to alternate positionsto control opening and closing of the main valve means, said cycle valvebeing movable to a position effecting closing of the main valve meansunder the control of fluid supplied to the cylinder, a first controlmeans coupled to the cycle valve including independently operable manualmeans and safety means actuated by placing the tool adjacent theworkpiece for moving the cycle valve to a position effecting opening ofthe main valve means only when both of the manual means and the safetymeans are actuated, and a second control means coupled to the cyclevalve and to the first control means for preventing movement of thecycle valve after the manual means and the safety means are operatedwhen the manual means is operated prior to the safety means.
 4. The toolset forth in claim 3 in which the second control means includes a fluidactuated piston mechanically coupled to the cycle valve and biasing thecycle valve against movement to a position effecting opening of the mainvalve means.
 5. A tool for driving fasteners into a workpiece comprisinga powered fastener driving assembly including a driver element actuatedby a drive piston movable within a cylinder, a fluid controlled mainvalve means for selectively supplying pressurized fluid to andexhausting fluid from the cylinder, a cycle valve coupled to the mainvalve means and movable to alternate positions to control opening andclosing of the main valve means, a first control means coupled to thecycle valve including manual means and safety means actuated by placingthe tool adjacent the workpiece for moving the cycle valve to said mainvalve opening control position when both of the manual means and thesafety means are actuated, a second control means coupled to the cyclevalve and to the cylinder for moving the cycle valve to, said main valveclosing control position, a fluid actuated control piston coupled to thecycle valve for controlling its movement, and means coupling the controlpiston to the first control means and controlling the control piston toprevent movement of the cycle valve to said opening control positionwhen the manual means is actuated prior to the safety means.
 6. The toolset forth in claim 5 including means mounting the control piston formovement into and out of engagement with the cycle valve.
 7. The toolset forth in claim 6 in which the first control means includes means forapplying a biasing force to the control piston to hold the controlpiston in engagement with the cycle valve to prevent movement of thecycle valve when the manual means is actuated prior to the safety means,said first control means rendering said biasing means ineffective whenthe safety means is actuated.
 8. A tool for driving fasteners into aworkpiece comprising a powered fastener driving assembly including adriver element actuated by a drive piston movable within a cylinderthrough power and return strokes, a fluid controlled main valve meansthat is opened to supply pressurized fluid to and that is closed toexhaust fluid from the cylinder, a cycle valve coupled to the main valvemeans and movable between a first position to control opening of themain valve means and a second position to control closing of the mainvalve means, a first control means coupled to the cycle valve includingmanual means and safety means actuated by placing the tool adjacent theworkpiece for moving the cycle valve to its first position when both ofthe manual means and the safety means are actuated, a second controlmeans coupled to the cycle valve and to the cylinder for moving thecycle valve to its second position when the piston has moved through itspower stroke, a fluid actuated control piston normally preventingmovement of the cycle valve to its first position, means coupling thecontrol piston to the first control means, and release means in thefirst control means for controlling movement of the control piston topermit movement of the cycle valve to said one first position only whenthe safety means is actuated prior to the manual means.
 9. The tool setforth in claim 8 in which the release means includes valve meanscontrolled by the safety means for selectively supplying an exhaustconnection and pressurized fluid to the fluid actuated control piston.10. A tool for driving fasteners into a workpiece comprising a poweredfastener driving assembly including a driver element actuated by a drivepiston movable within a cylinder, a fluid controlled main valve meansfor selectively supplying pressurized fluid to and exhausting fluid fromthe cylinder, a cycle valve coupled to the main valve means andcyclically movable to alternate positions to control opening and closingof the main valve means, a first control means coupled to the cyclevalve including independently operable manual means and safety meansactuated by placing the tool adjacent the workpiece for initiatingcyclic movement of the cycle valve between its alternate positions whenboth of the manual means and the safety means are actuated, and a secondcontrol means coupled to the cycle valve and the first control means forpreventing cyclic movement of the cycle valve after the safety means andmanual means are operated whenever the manual means is operated prior tothe safety means.
 11. The tool set forth in claim 10 in which the secondcontrol means includes a fluid actuated bias valve for applying a fluidbias to the cycle valve, and the first control means includes valvemeans for selectively connecting the bias valve to pressurized fluid andan exhaust.
 12. A multifire tool for driving a series of fasteners intoa workpiece comprising a powered fastener driving assembly including adriver element actuated by a drive piston movable within a cylinder, afluid controlled main valve means for selectively supplying pressurizedfluid to and exhausting fluid from the cylinder, a fluid operated cyclevalve coupled to the main valve means and movable to alternate positionsto control opening and closing of the main valve means, bias valve meansfor applying a fluid bias to the cycle valve means to move the cyclevalve means to one of its alternate positions, means coupled to thecycle valve and to the cylinder for applying a fluid bias to the cyclevalve means to move the cycle valve to the other of its alternatepositions, and control means including manual means and safety meansactuated by placing the tool adjacent the workpiece for initiatingmovement of the cycle valve when both of the manual means and the safetymeans are actuated, said control means including means operating thebias valve means to apply a fluid bias to the cycle valVe means onlywhen the safety means is actuated prior to the manual means.
 13. A toolfor driving fasteners into a workpiece comprising a powered fastenerdriving assembly including a driver element actuated by a drive pistonmovable within a drive cylinder, a fluid controlled main valve means forselectively supplying pressurized fluid to and exhausting fluid from thecylinder, a cycle valve coupled to the main valve means and movable toalternate positions to control opening and closing of the main valvemeans, said cycle valve including a valve cylinder and a valve pistonmovable therein for controlling the connection of exhaust andpressurized fluid to the main valve means, a piston means movable withinthe valve cylinder between a position biasing the valve piston and aposition spaced from the valve piston, first passage means placing thevalve cylinder in communication with the drive cylinder at a pointlocated between the piston means and the valve piston for applying afluid bias from the drive cylinder to the valve piston, second passagemeans communicating with the valve cylinder at a point spaced from thevalve piston to apply a fluid bias to the piston means only, and valvemeans controlling the application of fluid pressure to the secondpassage means.
 14. A tool for driving fasteners into a workpiececomprising a powered fastener driving assembly including a driverelement actuated by a drive piston movable within a cylinder, mainassembly means opened to supply pressurized fluid to and closed toexhaust fluid from the cylinder, cycle means coupled to the mainassembly means and movable to alternate positions to control opening andclosing of the main assembly means, a first control means coupled to thecycle means including means controlled by independently operable manualmeans and safety means actuated by placing the tool adjacent theworkpiece for moving the cycle means to a position effecting opening ofthe main assembly means only when both of the manual means and thesafety means are actuated, and a second control means coupled to thecycle means and responsive to the operation of at least one of themanual means and safety means for preventing movement of the cycle meanswhen the manual means is operated prior to the safety means.